Teletype measuring system



Nov. 25, 1952 L. M. CARVER TELETYPE MEASURING SYSTEM Filed Dec. 15, 1950 LA WEE/V6 5 M CARI/El? attorneys Patented Nov. 25, 1952 PAIE-NT GF-Fl TEIZETYPE"' MEASURING' SYSTEM Ii Lawrence MeflafiemStamford, Conn, assignor;

to L0- G,i,S,;-Laboratories, Inc.,- stamford conn a 0013poratiomofConnecticut Application December-13, 1950, Seria lNo. 200,553 1 This invention: relates :tother measurement 210i electricalpulses'and particularly to the -.measurlement of bias distortion:inateletypesignals.

must have the correct time k duration;-

the receiving apparatus -tvillinot -reproduce-an.

exact duplicate of-themessage that was transmittedz I Various typesof apparatushave "been proposed for measuring thispulse di'stortion; but the equip ment in general has been relati-vel-yt complex:

and expensive. Moreover, such delicate equlmment, which is also bulky 'vand heavypis not well adapted f for use in-portable orfield-=measuring instruments:

Other apparatus, suggested foruse in making: field measurementsi. requires th'at- =a special test E signal be; transmitte'di over: the tele'type lines while- :thedistortiom test is being made, thus; interrupting the#teletype servi-ce ove'r these -lines-.=

In accordancewithr the 1. present invention; a relativelyrsimplesand inexpensiveteletypedistor 'tion 'measuringsunit is provided which -does noti require the -transmissionzoi any special pulse signals-:duringrthe testiz. Theiinventiontreadily canr be incorporatedeinto .aa' lightzand compactl -unit entirely suitable iii-remaking field. measurements; theseemeasurements beinglm'ade while the lines areainsnormal:useesmthatzithere is' norinterrupti'on ofitherteletypeiservicei Thesvariouseobjects;z advantage-g1 and aspects of the present invention will be in part .ap parent from; and in: part :pointed out in, l t lreifollowing descriptionpf iaipreferred embodimentt-of theinvention considered in: conjunctionr'with-the accom panyingi drawing; which flsh'ow zal-diag'ram maticsrepresentatiorr .Offithl-l ielectricali circuits: of a sb'iasc-aiis'tortion measuringdnstrumentizemb'odye ing the inventi'o'na The;apparaizusvshhwn;in the d-nawingti-siadaptedfizozbeiconneoted directlyatol thejzincomingitelee. typev'lines 2: anal-"4. The :received teletypelpulses are applied to--=a--squaring device; generally indi cated i'at 6; which -re-sh'apes the incoming waves, as indicatedatll to form substantially square wavesyas indieated at- |2.

These "square-waves *are applied to a diifer entiating stage;generally-indicated at I4, which differentiates the square waves and rejects the;

negative pulses produced therefrom, the resulting sharp..;positive ;pulses, corresponding intime to theileading edgesaofrthe square-waves, being used to trigger a fone-shot multivi'brator circuit, generally indicated at I 6.5

Thelzpulses'or .squareawaves generated by the multivibrator, 1 I 6 a: are a diff erentiated: and applied multivibrator. pulses.

The squarewaves which; are delivered by the sq'u-ar-ing device '6 are also applied; after difier entiatingto, the r-coincidence detector Is -in; such manner; that it. responds: only-to the negative pulses coinciding int-time with the trailing: edges of the pulses produced by the squaringydevice 16.; The coincidence detector Ill-is arranged to deliver. 2. A signal only when the trailing edges of; the incomingpulses :coincide in time with the trailing edges ofv:the.-spulses from themultivibrator I 61. This condition of operation. can her-attained by adjusting. the length of the pulses generated by: the multivibrator |6-by meansmof a cont rol kno-b-l fl'provided for-this purpose;

In order .to. provide, a visual indication of the. coincidence got: the pulsesthe signals; from the coincidencedetector l8 are'utilized tor-trigger a; second? fone-shot! multivibrator, generally indie.v catedqati22. The pulses generated-rby the latter multivibrator circuit, which are ofimuqh'rlql duration athahgthe; narrow pulses used to-trigger this imultivibratorg are applied 1130': a: neons -lamp 2 4, whichrprovides .a .visual indicatiom whenever the, multivibrator -2 2 is operating,;-

Thus; with "the; pointer of knob- 20 adjustecl to. the zeroedistortionposition the neoni-lamp will. produce a continuously lblinkingdight indicating that;- the incoming; signals:- are ;notsubstantially distorted: If: the {neon .lampii'ails ;to::p.1tovi.de.-;;:a visual indication; the operator: -then:;mere1y, gad-l j-ustsxthe control knob 20 until the :neomdamp again providesavisual indication:andsthercalie' brations=2 6;- associated with the-control knob-20; will thenindicate the degree :of 1 space or-imark di-stortioninthe tletype signal-J Power -fo rthe teletype monitoring unit is' p'ro vided*-by-' a-- conventional-type power-supply; ln-' dicated in -block fo-im at=2 6; which-is connected toalt'ernating currentsupplylinesdB? The voltage-=deliveredby this' power s'upply preferably--15 regulated accurately so that variations in line voltage will not affect the accuracy of the measurements.

The detailed operation of the monitoring unit will be more clearly understood from a consideration of the following description of the particular embodiment of the invention illustrated in the drawing.'

The signals from the teletype lines 2 and 4 are applied across a voltage-divider circuit comprising two series connected fixed resistors 28 and 32. One end of resistor 28 is connected to a terminal 34 of a switch, generally indicated at 36, the other fixed contact 38 of which is connected to the junction of resistors 28 and 32. The movable arm 42 of this switch is connected through a series resistor 44 to the control grid 46 of a vacuum tube 48 of the squaring device 6. The switch 36 is provided so that the equipment can be utilized with either 30 or 60 milliampere teletype lines.

The anode 52 of the tube 48 is connected through a load resistor 54 to a positive-voltage supply lead 56 that is connected to an output terminal 58 on the power supply 26.

The anode 52 is coupled also through a fixed resistor 62 to a control grid 64 of a vacuum tube 66, a negative return circuit for the grid being provided through a fixed resistor 68 that is connected to a negative-voltage supply lead I2 from the negative output terminal I4 of the power supply 26. -The cathodes I6 and 18 of tubes 48 and 66, respectively, are connected through a common bias and coupling resistor 82 to one end of the fixed resistor 32 and through a grid-biasing resistor 84 to the negative supply lead '12, a by-pass condenser 86 being connected in parallel with the resistor 84. A resistor 85 connects between positive voltage supply lead 56 and the junction of resistors 32 and 84.

The anode 88 of the tube 66 is connected through a plate load resistor 92 to the positive voltage supply lead 56. The output signal from the squaring device 6 is taken from anode 88 and applied by a lead 94 to the differentiating stage I4 and to the coincidence detector I8.

In this particular embodiment, the squaring circuit 6 comprises a conventional vacuum-tube trigger circuit whose function is to modify the shape of the incoming waves, as indicated at 8, to produce square pulses, as indicated at I2, the latter pulses having duration times equal to those of the respective incoming pulses. Other devices, for example relays, may be used to perform this Squaring function. In those instances where the incoming pulses have a sufiiciently square shape, the squaring device can be omitted. However, in commercial equipment where the rise time or the signal to be tested is unknown, it has been found desirable to include the squaring device. The pulses from squaring device 6 are applied to a difierentiatin circuit comprising a condenser 96 and a resistor 98 connected in series between the anode lead 94 and the negative voltage supply lead I2. The junction of the condenser 96 and resistor 98 is connected to the control grid I02 of a vacuum tube I04, which is arranged to respond selectively to the positive pulses. The anode I06 of this tube is connected directly to the positive voltage supply lead and its cathode I08 is connected through a cathode load resistor II2 to the negative-voltage supply lead I2.

The difierentiation of the square waves I2 produces a series of positive pulses of very short duration each corresponding to the leading edge of one of the square waves I2, and a series of similar pulses of negative polarity each corresponding to the trailing edge of one of the pulses I2. The tube I04, however, is operated at outofi so that plate current does not ordinarily flow in this tube. The negative pulses, therefore, have no effect on the operation of tube I04, but the positive pulses are transmitted by the tube, and are coupled from the cathode I68 to the multivibrator circuit I6.

These positive short duration pulses are applied to the control grid II4 of the first multivibrator tube I I6, this grid being biased positively by a connection to the junction of two fixed resistors H6 and I22, connected in series between the positive-voltage supply lead 56 and the negative lead 12. The anode I24 of this tube is connected through a load resistor I26 to a positive voltage supply lead I28 that is connected to a positive terminal I30 of the power supply 26.

The anode I24 of this tube is coupled also through a coupling condenser I32 to a control grid I34 of the second multivibrator tube I36, D.-C. return path for the grid I34 being provided through a fixed resistor I38, a variable resistor I42, and a fixed resistor I44, connected in series between the control grid and the negative lead I2. The cathodes I46 and I48 of tubes H6 and I36, respectively, are coupled to the negative lead 12 through a common bias and coupling resistor I52. The anode I54 of tube I36 is connected through a voltage-droppin resistor I56 to the positive voltage supply lead I28. 1

A positive bias voltage is applied to the control grid I34 of tube I36 by means of a fixed resistor I58 and a variable resistor I62 connected in series between the positive voltage supply lead 56 and the junction of variable resistor I42 .and fixed resistor I44.

This multivibrator I6 is of the one-shot type so that each time it is triggered by an incoming positive pulse it will generate a single square wave and then return to its normal stable or off condition until again triggered by an incoming pulse. The duration of the pulse generated by the multivibrator I6 is determined primarily by the values of the capacitor I32, and the resistors I38, I 42 and I62. Accordingly, the resistor I62 can be calibrated in accordance with the duration of the pulses generated by the multivibrator I6, and the control knob 20, therefore, is arranged to control the setting of the resistor I62. The indicating marks 26 associated with the pointer of knob 20 are calibrated to indicate the bias distortion from 50% mark to 50% space bias distortion. This represents a change in pulse length from 11 milliseconds to 33 milliseconds, where 22 Znilliseconds is the equivalent of zero bias distorion.

The multivibrator. pulses appearing at anode I24 of tube II6 are coupled by a lead I64 to the coincidence detector I8 where they are differentiated by a series-connected condenser I66 and a fixed resistor I68. The junction of the condenser and resistor is connected to the control grid I12 of the coincidence detector tubeI'I4.

Thus, the one-shot multivibrator and its differentiating circuit forms an effective manually controllable time delay circuit This will be clear upon consideration or the fact that the multivibrator pulse is not utilized as such except for the purpose of generating a differentiated pulse similar to the pulse that triggers the multivibrator. Thus, an applied pulse triggers the multivibrator I6 which generates a single square --gridl2l.8 .of. the tube .I96lwhich is connected also pulsefgfhavinggia slen'gtlr-oritime'duration -depends ent?upon"= the. circuit constants; The *difieren tiatinggcircuit includin'ggthe condenser i I 66 and resistor; llirdifierentiates" this" squarei'pulseranw proddc'es' a pul'se coincidentintime with thetrai1*-"- 5 denser I I6 and llagfiited "resistor: I 18' connected l5 The anode I84 of 'the coincidence tubell'l lffls coupledlthrough, a...plate .loading inductor I 351w therpositixie ivoltage supply le'adfi 6'. l Affi'xed ('re-. sister ;I 86 is? :connected. 'hetween,..th'e -positivevolt; age-supply; lad 5'6 and'thecathode I82, andwith thescathbdelresis'tor I I8 forms "a voltage-dividers circuit; thatwbiases the coincidence-tube I Illbe- 7 yondicut-oifl This-bias voltage is: such-that apositive pulse applied :tothe. .gridlll 12,- or a negative pulse applied tolthe cath'ode' l 824 both of the magnitudes-- delivered-l by. the: respective circuits), wills not: causecurrent teiflowl-through; the tube I I 4'. How- 7 ever, if: at the instant, I a positive pulse applied torgrida I 12, av negative-pulseis 1applied; simultaneo'usly; lto the-cathodezl 82', the combined efiects of: jthe-pulsesawill be suificient to: cause plate current t0-:fl0w;in-.this:tuba;. That is, it the trailing; edgecofa square wave-delivered by';the-squaring device 6 icoincidescin timewwithi the. :trailingiedge ofiia ulseigeneratedgbygthe multivibrator'circuitj I 6;; puls'eatof, plate currentuwill flowsthrough the tube I14. Tube I14, therefore, delivers aseriesof. pulses-whenever the; pulse lengthsot: the incoming signals correspondtogthe pulse lengths vof the; sige; nalsz eneratedzby zthe :multivibratcir .I 6

These pulses of; 'currentrthroughxthe :tube I14 are-, oiasuchi shortxduration:;that:.they:will not: produce; a'zsatisfactory indication: fromrthelneon" lamp ,2 4-,aandpaccordingly; zare :utilized;;.to trigger another; oneeshbtf multiviloratorx: or; pulse-t, lengtheningpircuitzn.

, The pulsesaappearing ;at theIarmder I 84 .of' the coincidencettube l 1'4 are'icoupledithrougha cone,

denser 1882M! thexcontrol gridil 92iof armultivi= brazton tuber-I 94;;1' a rgrid returni-circuit :bein'g provided tby va; resistorm I 96 zconnectedtbetween' the controllgridil 92 ,amh'supply lead 12.1 This? multi'-" vibrator 'icircuit; talscitincludesza i second :tube 1 I 9 6 inzacircuit-similantcthat descri'bed in connection with-multivibratoril 6: The cathodes'il 98 and 20-2 ofzltheseztubes are connected through' 'a :common resistor1r20'4 ito:-thenegative I supply lead 112, and the "-anode's: 206iandfi2fl8 are 2 connected through platdzresistors-i2 I ii -and: 2 I 4 respectively,- to the positive voltage' -supply =lead =5BJ The anode-L206 is coupled through a condenser 2I6 the control through aresistorinto' the positive voltage supply lead 56.

The. neon ,lamp iindicator 2 4 is. connected hetween-the anode 208 of'tube 96.;and atnegative supply lead 12. The tube I96 draws current when the multivilirator 'is in its -O'fi condition, so that the voltage applied to the 1160111811111) 24 is-insufii-' cient to-iignite itiv However-,z-when an incoming pplse-issupplied to the multivibrator circuit32-2, theaplateecurrent in tube I96- visccut OfiiEfOtlthe 7 6 duration ofi the"pulse "generated'bythis "multivibrator and the neon lamp 24 accordingly -ishereinbefore "set fortht and jthat it 'can' -be ecc=- nomicallvmanufactured since-theseparate? cam ponents are *readili available 'from"commercial sources:- Moreover, it' is apparent" that *a varietyi:

sirab1e in ""adapting the invention for particular? applications may be mad w without* departing from the 'spi-r'it of' the '-*invention--* or*-"thescope- 0fthe -claims -hereinafterset*fcirthi It is to the understoodfi also? that*certain featuresi of the inventionmavbe at times utilizedito advantage without a corresponding use of other faturesr g 1." A teletypedistortion monitoring system+ comprising --a pair of transmission lines-carry?- ing -te'1etype signals "WhbSe distortion is? to be measured,-a"trigger-circuit coupled .to said trans mission lines and responsive'to "said "signals inrgenerating square waves "having timedurations equal to correspondingiteletypesignals" and sub stantially coincident in time therewith; a vfirst" resistance-capacitance differentiating circuit: connected to the output" "of said trigger-circuit?- apulse-selection circuit-coupled to -sai'dttfirst diiferentiating circuit and responsive' se'lectively to positive pulses" delivered thereby: a'"first*'one=-i shot multivibrator -cir'cuitrunderithe "control iof said pulse-selection 1 circuit" and including 'a ivarii able resistor for i'controlling'the' duratibn of pulses produced. by: said multivibrator 'circuit; a second resistance=capacitance difierentiating network coupled 'to l the output of "said 'multi-a vibrator," a" third resistance-"capacitance *difi'er-i" entiating' network coupled to the output of "said trigger ',circuit,-a' coincidence detector including a vacuumtube having a control grid1couple'd'to'said' second differentiating network and a cathode coupled to'said third differentiatingnetwork, and

1 a source ofpositive bias voltageccnnected to said the reception of a l negative pulse .at said cathe,

ode, a second one-shot multi-Wibrator.connected toxsaid coincidence tube andiarranged-jto'l be triggered by. the flow of plate currentthereimand? a neon-lamp indicator .coupled' to the outputjoi said multi-vibrator and arranged to indicate.

when 'said variable resistor has beenlmanually, adjusted in accordance. with the. distortion of said teletype'signals";

2;A1 teletype distortion, monitoring system. comprising a pair of, transmission. linesicarrying'. teletype pulse. signalswhose distorticnlis..,td.ibe, measured, a wave-squaringlcircuit couple'd to-said" transmission lines for squaringmuplthe. leading. and trailing edges of ."said. signals;apilrst'ldifieheentiating circuit connecteditot .th'e. .ou-tputbf said trigger circuit, ,a pulsesele'ction circuitpcoupled' to said first differentiating. circuitl'and responsive selectively to positive .puls'es ldelivered thereby; at firstljsquare-wave generator under thencontroluofz said pulse selection .circuit and including .a vari-; able resistor, for. controlling; the duration, of. pulses produced lo'yv said generator, Ia second-ldif ferentiating' network coupled to-xthe: output ofsaid gfiI'SU generator,-v a zthild differentiating 3118i;- Worklcoupled .to, the outputoi'saidmaveesquaring circuit, a coincidence detector including a vacuum tube having a control grid coupled to said second differentiating network and a cathode coupled to said third differentiating network, and a source of bias voltage connected to said vacuum tube and of sufficient magnitude to bias said tube beyond cut-01f, said tube being arranged to draw plate current only when a positive pulse is received by said control grid simultaneously with the reception of a negative pulse at said cathode, a second square-wave generator connected to said coincidence tube and arranged to be triggered by the flow of plate current therein, and a visual indicator coupled to the output of said second generator and arranged to indicate when said variable resistor has been manually adjusted in accordance with the distortion of said teletype signals.

3. A teletype distortion monitoring system comprising a pair of transmission lines carrying teletype signals whose distortion is to be measured, a first differentiating circuit coupled to said transmission lines for generating signals coincident in time with the leading and trailing edges of the teletype pulses, a pulse selection circuit coupled to said first differentiating circuit and responsive selectively to positive pulses delivered thereby, a first multivibrator circuit including a variable element for controlling the duration of pulses produced by said multivibrator circuit, means under the control of said pulse selection circuit for synchronizing the operation of said multivibrator with said teletype signals, a second difierentiating network coupled to the output of said first multivibrator, a third differentiating network coupled to said transmission lines, a coincidence detector including a vacuum tube having a first control element coupled to said second diilerentiating network and a second control element coupled to said third differentiating network, and a source of bias voltage connected to a control element of said tube and arranged to bias said tube beyond cut-off, said tube being arranged to draw plate current only when two pulses of predetermined polarity are received simultaneously by it, and indicat ing means under the control of said coincidence tube.

4. A teletype distortion monitoring system comprising a teletype receiving station, a pair of transmission lines connected to said station and carrying teletype signals whose distortion is to be measured, a first differentiating circuit coupled to said transmission line for generating signals coincident in time with the leading and trailing edges of the teletype pulses, a pulse selection circuit coupled to said first differentiating circuit and responsive selectively to said signals coincident in time with the leading edges of said teletype pulses, a signal generator circuit coupled to and under the control of said pulse selection circuit for producing control pulses of short duration relative to the duration of said teletype pulses, means forming part of said signal generator for establishing a manually adjustable synchronization relationship between said control pulses and the leading edges of said teletype pulses, a second differentiating network coupled to said transmission lines, a coincidence detector coupled to said second differentiating network and to said signal generator circuit, said detector being arranged to draw plate current only when two pulses of predetermined polarity are received simultaneously by it, and indicating means under the control of said coincidence tube.

5. A teletype distortion monitoring system comprising a pair of transmission lines carrying teletype signals whose distortion is to be meas-' ured, difierentiating means coupled to said transmission line for generating first control signals coincident in time with the leading edges of the teletype pulses and second control signals coincident in time with the trailing edges of said pulses, a first time-delay signal-generating circuit responsive to said first control signals and arranged to produce third control signals delayed intime with respect to said first control signals, said signal-generating circuit including a manually adjustable element for controlling the delaytime between corresponding pulses of said first and third control signals, a coincidence detector, circuit means coupling said second and third signals to said coincidence detector, and indicating means under the control of said coincidence detector. 1

6. A pulse duration measuring system comprising first circuit means responsive to the leading edges of incoming pulses whose distortion is to be measured, second circuit means responsive to the trailing edges of pulses to be measured, a coincidence detector responsive selectively to two simultaneous pulses of predetermined polarity, pulse generating means under the control of said first circuit means for producing control pulses having a substantially shorter duration than said incoming pulses, said pulse generating means in cluding time delay means whereby said control pulses occur a predetermined interval after the leading edge of each incoming pulse, manually adjustable means for controlling said time delay means to vary the time interval between the leading edge of each incoming pulse and the next subsequent control pulse, means coupling said second circuit means and said control pulses to said coincidence detector, and indicating means for denoting the operation of said coincidence detector.

7. In a teletype system, apparatus for measuring the distortion of incoming teletype signals comprising differentiating means coupled to said teletype system and responsive to teletype signals for producing pulses coincident intime with the leading and trailing edges of the' teletype pulses whose distortion is to be measured, circuit means responsive selectively to the leadingedge pulses produced by said differentiating means, a coincidence detector responsive selectively to two simultaneous pulses of predetermined polarity, pulse generating means under the control of said circuit means for producing control pulses having a substantially shorter duration than said incoming pulses, said pulse generating means including manually adjustable time delay means whereby each of said control pulses occurs an interval of time after the'leading edgeof each incoming pulse, connecting: means coupling said trailing-edge pulses produced by said diiferentiating means and said control pulses to said coincidence detector, and indicating means for denoting the operation of said coincidence detector.

LAWRENCE M. CARVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

